And it's really meant to be solved using constrains if we want to avoid calculations :
Here is a way to solve it using Freecad :

HI Pilou,

Indeed it is... Please forgive my English for misconceptions.

No problem! :) English is not my cup of tea too! :)

Hi Mip,

Thank you very much for pointing this up!
I'll let know my nephew about this FreeCAD.

Cheers!

Hi Elang,

Here is a short animation showing how to achieve it with Freecad's Sketcher Workbench.
(Grid snapping and Auto Constraints are deactivated)

I must add that, even if resolving this particular problem is very easy with Freecad's Sketcher Workbench,
I still highly prefer using MoI for every other concept or presentation drawings, 2D or 3D.
Freecad is interesting but not nearly as fast, intuitive and stable for Moments of Inspiration...
Even if it is Parametric, most of the time, I find it faster and simpler to redraw with MoI.

Hi VINC,

Thank you very much for pointing this up.

And, I completely agree with you and did tell my nephew that Moi is a great app which he confirmed. He even promote Moi to his colleagues and willing to give them basic tutorial for free.

Cheers!